The first order of business when cooking a duck is to trim away any skin that overlapping the meat. Next, you want to score the skin in a crosshatch pattern as I have done below. Leave about a 1/4 inch between slices of the knife, and be very careful not to cut into the meat. The crosshatch pattern will ensure that the skin crisps up as the duck cooks. Once you have scored the skin, pat the duck dry with paper towels.
Now, for the seasoning. If you are going to make a sauce to serve with the duck, the duck needs little more than salt and pepper on both sides. However, I prefer to serve duck sauceless, letting the rich flavors of the duck meat stand out on their own. Using a recipe from Thomas Keller's Ad Hoc at Home
Once you are ready to cook the duck breast, preheat the oven to 400F. Depending on how many duck breasts you are cooking, use a large skillet or two large skillets that will comfortably hold the duck breasts with plenty of room to move them around as they cook. Add just enough canola oil to coat each skillet and heat the oil over medium-low heat. Add the breasts to the pan, skin-side down. Let them cook until the skin is nicely browned and crispy, about 17 to 20 minutes. Periodically check on the doneness of the skin and move the duck breasts to different parts of the pan to ensure that they evenly cook. Also, occasionally pour out the fat that collects in the pan so that there is always no more than 1/4-inch of fat in the skillet. Duck fat is delicious to cook with, so save it for a later use.
Once the skin is cooked, flip the breasts and sear the meat side for a minute. Flip the duck breasts once again so that they are skin-side down in the pan. Finally, pop each skillet into the 400F oven and cook the duck breasts until they are medium-rare, about 5 minutes. Remove the duck breasts from the oven and place them on a plate. Tent the plate with foil and let the duck breasts rest for 5 to 10 minutes to allow them to reabsorb the meat juices. Slice each duck breast against the grain into thin slices and serve them immediately.